1. Field of the Invention
The present invention relates to an observation optical system, and a microscope using the observation optical system, and more particularly, to an observation optical system including afocal parts having a large amount of extension, and to a microscope using the observation optical system.
2. Description of the Related Art
In recent years, microscopes have been used in various fields, and observation operations using a microscope have been performed for a long time in many cases. Accordingly, to enable an observation causing no burden to an observer's posture, a function of adjusting a position of an eyepiece lens (hereinafter referred to as an eye point position) that an observer looks through in accordance with his or her body is demanded for microscopes.
Examples of various microscope configurations that can adjust an eye point position that have been proposed to meet such demands include Japanese National Publication of International Patent Application (Kohyo) No. 2004-530948, Japanese Laid-open Patent Publication No. 2006-292831, Japanese Patent Publication No. 4035509, and Japanese Laid-open Patent. Publication No, 2001-264636. These patent documents propose configurations for implementing an eye point position that is optimal for an observer by adjusting any one or a combination of <a> an eye point position in a vertical dimension (for example, a distance of a microscope from the surface of a desk to an eyepiece lens of the microscope in the vertical dimension), <b> an eye point position in a horizontal dimension (for example, a distance in the horizontal dimension from a focusing handle to an eye point position), and <c> an angle of an optical axis at an eye point position (namely, an angle at which an observer looks through an eyepiece lens; referred to hereinafter as an angle of depression).
Specifically, Japanese National Publication of International Patent Application (Kohyo) No. 2004-530948 discloses a configuration for adjusting <a> an eye point position in a vertical dimension. Japanese Laid-open Patent Publication No. 2006-292831 discloses a configuration for adjusting <a> an eye point position in a vertical dimension, and <c> an angle of depression. Japanese Patent Publication No. 4035509 discloses a configuration for adjusting <b> an eye point position in a horizontal dimension, and <c> an angle of depression. Japanese Laid-open Patent Publication No. 2001-264636 discloses a configuration for adjusting <b> an eye point position in a horizontal dimension, <c> an angle of depression, and an eye point position coaxial to the angle of depression. With the adjustment of an eye point position coaxial to an angle of depression, <a> an eye point position in a vertical dimension and <b> an eye point position in a horizontal dimension can be simultaneously adjusted at a certain ratio according to the angle of depression.
With the above described adjustments of <a> and <b> but not <c> the adjustment of an angle of depression for rotating an optical axis with a rotation mechanism, an optical path length is changed. Normally, with the adjustments of <a> and <b>, the entire optical path length is changed by extending/contracting an focal part passed through by an afocal right flux that does not affect an image forming position. With the extension/contraction of the afocal part, an eye point position is adjusted.